You go girl. I'm having flashbacks of the beginning of our journey. Except you are moving at breakneck speed. Be careful, don't break your neck. I have a couple of things to add. Don't miss the forest for the trees. This may take a while so don't be discouraged.
Regarding holes and cracks. As has already been stated, fiberglass is a wonderful thing. Im really glad that you have a friend to help you. That alone will give you peace of mind that you are doing it correctly. I think that I mentioned to you in a pm that our trailer/ frame had some broken places that we may not have seen. Our camper is put together differently that yours. When we took the floor out, the frame was completely exposed from the top. We still had to lift our shell to get the trailer out.
If you have a way to lift your shell and examine (and while it is off sand and paint) the trailer you will be sure to find any problems. Not sure where your trailer meets the shell that should be the only place that you need to support. We used 4 jacks, concrete blocks and some 2x4s to support our shell. Once the trailer was out we lowered the shell to a safer height.
I think you are already doing this, but try to determine the origin of all holes and cracks. There could be a rub from a problem elsewhere that will return if you dont address it now.
That band across your ceiling looks like something added post factory. They may have been trying to fix a sag. Lots of these little guys sag and that in its self can cause lots of mysteries. Maybe you could determine if there is a problem with sag by measuring floor to ceiling in several places. I see that you have ceiling supports in place, if you put them at the height of the existing ceiling you may still be able to determine. If not possible now, when you reassemble be aware. when we reassembled we fiberglassed wood cleats to reattach our cabinets and closest. We also added some additional supports (in a decorative manner). I think this helped reinforce our structural integrity.
I too wanted to close up every single hole that could possibly leak. And we did! We had to make fresh holes for electrical
and ceiling venting. We used a 3M heavy duty double sided tape it to install the awning
track, the drip guards, and our outside door swing stopper, not sure what it's called. They are still working great with no sign of failure, and I put a lot of tension on that awning
Try not to sand silicone. Remove as much as you can with a blade. Then wash with denatured alcohol keeping the rubbing place as small as possible, before you sand. Nothing sticks to silicone. I think Donna told me that.
Prep every surface properly. Follow directions on product, no shortcuts. Preparation is key for materials to function at their best.
Be safe...eye protection, skin protection, lung protection, ear protection.
If you can.... beg, borrow or steal somewhere indoors to work thru your winter. It will help you maintain your momentum. Ok, don't steal.
I haven't said much, if anything, that I didn't learn from the great people on this forum. I think you may ask as many questions as I did. Questions are good, that's how we learn. They were patient and kind. Hey, I just realized I'm one of you guys now.
I can't offer as much as some but I got a little to give! Some opinions vary. Consider everything, take what works for you, and leave the rest.
I'm excited for you and look forward to following your progress.