What you are describing is, the bottom wall stud band board and possibly, the bottom floor band board is rotted and not able to hold lag screws etc.
Your older camper I do believe is made where the walls studs/wall frame is attached to the side floor system. The later built Sunlines, the walls are on top of the main floor. The "how to" repair for both is similar when they rot out.
It would help if you can post a few pics of the side of the camper showing bumper to front wall and down at the awning mounts.
Without pics I'm going to use generic terms as I have not personally seen your model up close and personal.
What you need to do is, remove the bottom piece of siding where the awning brackets bolts mount through then rebuild the rotted with good wood. In order to get the siding off, you need to take certain other items mounted over the siding off first.
Going from only a floor plan in the 84 brochure on your T1450 I'm estimating these items have to come off first.
For the front awning mount:
Unscrew the front right corner molding about 3 to 4 feet up the camper starting at the bottom. You can remove the entire corner if wanted and it is a good thing to do to reset the old dried up putty tape seal corner anyway.
If the corner molding is only loosend 3 to 4 feet, tip outward the corner molding to expose the staples on the bottom front siding sheet at the corner. You have to warm the old putty tape up with a heat gun before peeling away the corner molding. Pry gently until it releases and only move it enough to get to the front siding. The staples are under any old putty tape to be scraped off.
The front siding is put on "after" the long side wall siding is installed. Along the bottom of the front wall are some screws that hold the bottom of the bottom siding sheet on. Remove about 3 feet of them from the corner.
Dig through the old putty tape in the corner and find the staples holding the front sheet to the camper wood corner. Remove them up about 1 1/2" sheets of siding from the bottom of the camper. Warm up the siding and gently pry the front siding back enough to expose the long front right wall siding that is most like folded over the corner wood. Now, dig out the putty tape on the right side sheet and pull the staples out of the right side bottom siding sheet. This only loosens up the front corner siding attachment.
Odds are high, you have to pull out the entry door as the door flange goes over the bottom piece of siding. Remove the door bottom threshold plate. Remove all the screws in the door frame to the siding, heat gun warm up the door frame where the screws are, work in an all sides dulled surface steel tool, a stiff blade putty knife or old dull wood chisel etc. and start at the bottom and pry and heat until the door frame starts to come off the siding. Work it slow and on both front and rear sides. It will start to come out, keep heating and prying and it will come out.
Now, look under the camper at the bottom piece of siding. I'm not 100% sure how a 1984 Sunline attached the bottom piece to the bottom of the floor. All the newer ones, the siding is folded under the camper with a 90 degree bend and stapled up from the bottom into the wall/floor joists. Pull those staples. Pull out any staples on the ends of the bottom piece of siding behind the door frame molding. Once all the staples are out, the bottom piece of siding will come off exposing the rotted wood.
Your may have a metal bottom cover, you will have to undo enough of the bottom cover to expose the bad wood that needs fixing. It may only have to be pushed down locally in that area.
Once the bottom siding is off, you can see and repair the bad wood. Heads up, be prepared for water damage beyond the awning bracket. The window frame above the front right awning bracket, the door frame, the front right corner molding and a roof leak are all suspects on water from above that ended up at the bottom of the wall to rot out the wood holding the awning bracket. You can access the damage when the bottom siding is off.
If you want to access water damage in the walls, floor or ceiling before taking anything apart, consider getting a moisture meter and scanning the inside walls etc. This may help you decide what to to. See here for more on the meter https://www.sunlineclub.com/forums/f...per-17613.html
This post may help. This is from a 2004 Sunline taking the front right corner apart and the whole front wall. This vintage is built with the walls on top of the floor but how the siding comes off is very similar. https://www.sunlineclub.com/forums/f...2-a-18706.html
This post is from a 87 camper and the front is all apart from Thomascine, it may help also as the way the floor is made is closer to yours https://www.sunlineclub.com/forums/f...air-17458.html
Here is another 87 camper all apart from Yellow Jacket https://www.sunlineclub.com/forums/f...ion-19403.html
We are here to help on how to put it all back together and seal it up. Just ask if you cannot find what you need.
Hope this helps