OK, so you have options at the moment since you have not mounted it yet. Here are some thoughts to consider, I'll go into more depth with pics even, if you want to pursue one of these options or others when the time comes.
1. The cable going up the fridge vent, mechanically that is possible. There are some things to check though, I'm not a WFI extender guy so I do not know, but I know the camper. The fridge roof vent sees a good deal of heat coming off the rear fridge coils. The boiler area can see 700 deg F at the point of heating the boiler tube. The top coils up high near the roof can see 150 deg F on a regular basis. This was all measured in an open bench test at 55F room temp. See here for the test. This is the same fridge you have, this is 2004 T1950 I was restoring. https://www.sunlineclub.com/forums/f...tml#post154885
On a hot summer day, when it is 85 to 90 F outside, the heat going out the roof stack could be a lot hotter then the 150 F I saw in the barn bench test.
I'm not sure if heat affects the working of the cable to the antenna or the working of the system. Most wire has an insulation casing working temperature rating that should not be exceeded. Point being, make sure you check what the cable is rated for heat wise and does not affect the signal transmission before going the fridge vent route. A call to the manufacture may be able to rule this out as a problem or tell you it will be a problem.
2. Mounting the antenna to the roof, your 2004 Sunline has the Sunline rubber roof. Unless yours was one of the very few custom ordered Sunlines, the travel trailers have "non walk on" roofs. Meaning there is no full wood decking on the roof to hold a persons weight without special precautions being taken. Small plywood pieces over the rafters with a tarp or other methods on the rubber to prevent abrasion needs to be used while servicing the roof.
When Sunline mounted a roof item, like the crank up Wineguard antenna or the Jensen radio antenna, or anything else on the roof, they added local OSB board reinforcement under just for that item to hold the screws. Every where other then over a rafter is just a bud board nick named heavy corrugate fiber board product I believe might be product called Unicore. The bud board area cannot be screwed into or walk on without breaking it.
That said, if you want to go the roof mount route, you need to screw the antenna into a rafter or other existing OSB reinforcement. When you get the antenna bracket, post a pic and some dimensions and I can help better. You want to seal the bracket to the rubber using butyl sealing tape. Then screw through the butyl, then cover the screws and the outer perimeter of the bracket with Dicor Self leveling lap sealant. Clean the roof well before mounting.
I'm not sure how the cable attaches to the antenna, so I can't help on that not seeing how to fits.
This link will take you to a post with pics of the rafters that yours will be like once the rubber membrane/bud board combo if taken off and the insulation is off. https://www.sunlineclub.com/forums/f...tml#post151483
3. Here is a new option for you. This option may help if the fridge heat affects the operation of the cable and or you do not want to mount the antenna on the roof after reviewing.
I'm not totally sure how the WIFI extender will be affected or not as the tip of the antenna is not the highest point on the camper, but it is an option for mounting the antenna and how to get the wire into the camper. Our first Sunline was a 2004 T2499, we really liked it, then we found the T310SR which is very close to the same floor plan but bigger and with a slide. I know the T2499 well, I even have a 2007 T2499 half apart now in the barn as a project camper I will restore, well some day in the future.
Go to the left side of the camper and open the cargo door to the peg board storage area. That large cargo door could hold the antenna with some reinforcement added to the inside of the door. The cable can go through the door, be sealed to the door, and attach to the antenna. The cable would be flexed in a loop with the door hinge so the door opens and closes without issue. There is room up high or where ever you want in that peg board area to put the other end of the control system the antenna cable plugs into. Or you can run the cable up into the over the sink cabinet, or under the sink cabinet, there is a lot of excess room under the sink behind the draws. There is live 12 Volts DC going to the furnace or the water heater that you can tap into providing the amperage needs are small. That wire feed can get back into the under the sink cabinet or up into the peg board area, or up above the sink area.
If this option has any interest, I can sketch out at least one method on how to mount this to the cargo door and deal with the cable. Seeing the parts would also help. By going the cargo door route, assuming the antenna would still work, you are not dealing with the roof.
4. Another option which is a spin off of option 3 above, it to mount the antenna to the left side of the camper just under the gutter rail. The top of the antenna could/would be above the roof line. You have to find the wall stud to mount the antenna too, then you have to drill a hole through the siding and into the top of the peg board cargo area. We would want to install a plastic sleeve in the hole to not cut the cable with the siding edges and get the connector through it. We then have to seal the sleeve to the siding and the cable to the sleeve or use a grommet clamp waterproof cable fitting. The risk is the size of the hole in the siding for the sleeve to get the cable though the sleeve. The siding is very thin, if can be drilled hole/ sawed, but it will take care and need to be slow to not create an issue with the hole in the siding ripping.
Once the cable is into the peg board storage area, then do the same as option 3 above with the control board/power routing etc.
You will need to use the butyl tape again to seal the antenna mounting bracket top the siding, then use Proflex RV sealant to seal the bracket, the sleeve and the cable. If this option has interest, I can show this in pics of the wall assembly and how to create the sealing of the bracket.
5. There are ways go up through the roof with the cable, ideally with no connector on the end cable so the penetration is smaller. The issue is, you have to drill up through a rafter or be by the Wineguard antenna area as there is OSB in the Wineguard area to screw too to mount the water tight fitting you need to make to seal the cable. This whole option can fall apart if the hole for the cable has to be much over say, 1/2". Is the cable a standard coax cable connecter that can be cut off, poke the cable up through a 3/8" hole, then through a water proof sealing electrical fitting on a roof flange above the roof line, then crimp on a new connector?
Think this over, and ask away for more on any of the info I commented on. Or other ideas you may come up after reading.
Option 3 would be the possible front runner idea if the cable cannot handle the heat of the fridge assuming the system works on the side of the camper below the roof line.
Hope this helps,