How old is the camper, what year? Since you have the galvanized ramp it is a 2004 or older most likely.
I have used flex mend to seal a joint on the slide floor. Just I applied it full width and up over the tongue inside on purpose so there is no edge to pick at when coming in. Gentle hair dryer heat and press to seal it permanently.
The seam I am covering
Start applying and leave paper on to only peel as you go
with the slide lifted slightly, get it inside
Once inside, pull tight and peel paper and start to fold over.
folder over and cut off. The metal plate is off in this pic, flex mend under it
On yours, make sure any fraying edges are trimmed off. You need a flat smooth area to patch over.
Now what caused the tear? Some possibilities
1. Look at the trough in this area for a shiny spot. If there is one on the ramp, that shinny spot is a high spot and that concentrated a lot of pressure in the one spot and wore the Darco. tap it down gently and do not go over deep or it may swedge up a metal creating a bigger issue. Just tap until flush. Use plastic dead blow hammer if you have one or block of hard wood and hammer. Ideally not steel hammer directly.
2. Is a dirt spot on the bottom of the floor in this location creating abrasion? Once the tear starts, use over time will work on it making it longer.
3. Some how that spot ended up getting more pressure then the other areas. Is there a heavy object over the area? A real heavy draw under the dinette etc? The Darco will not last forever and eventually wear. Mine is now 10 years old and still OK. And I have used the camper a lot. I know some day I will have to deal with this more than may patch above.
To help prevent the issue or slow it down once started, spray the trough edge with liquid silicone to help lower the friction. This will help but it does wear off over time so you need to add it back on.
A longer tear anti friction method is to use UHMW tape. This is a tape you put on the trough to cut the friction. McMaster-Carr
It is not cheap and the thicker the longer it lasts. Use the 6" or 12 wide and go over the tough hump. As far as thickness, 0.012, 0.022 or 0.036" The thinner is too thin and the 1/16" might not flex enough to stay stuck down. Scroll down they make super bonding tape too. I do not know if you need this, it was not listed a few years ago but it sounds like it sticks better.
We use this at work on all kinds of things to cut sliding friction.
I helped a fellow SOC member with this on his big heavy 5er slide. The report was it worked really good when he put it down. This was now about 2 maybe 3 years ago. I do not have any follow on data to know how long it lasts. I myself was going to try this on mine to cut down on the power draw and have the slide come in easier. I just never made it to it yet. For sure if you do this, the metal has to be clean and alcohol, brake cleaner, acetone cleaned so the cleaner flashes off and leaves no residue so the tape can stick.
And for sure make sure the wrap is wide enough to not have the floor catch an edge of it and start peeling it up.
Can you post a pic or too so we can see how wide the tear is? Measure it too. A 1/8" tear is a lot different than 1" wide on how we may fix this.
Hope this helps