Welcome to the forum. Sorry to hear about your fire damage.
Repair costs are "all over the place" depending on so many variables that it's impossible to even guess what it might cost in any given location at any given time of the year...
About the only option, assuming you have insurance on your trailer, is to turn it into your insurance, have them run the costs and determine if they would even consider a repair.... Most insurance companies have a "max repair percentage of actual value"... If the repair cost exceeds their "replacement cost" then they won't approve a repair and will "buy out your trailer at the present value"..
On a 2008 model trailer, the actual value may be significantly less than what you consider to be its value. So, have you talked to your insurance company to see if they will even consider a repair? It sounds like with the fire damage, there's likely also going to be "scorch marks/decal damage to the rest of that side of the trailer and also likely to be some damage to the EPDM/TPO roofing membrane on the main trailer, as well as to any plastic attachments on the trailer sidewall.
You may be looking at far more to repair than the insurance company will approve, so at this point, if you haven't got your insurance company involved, I'd suggest that as a next step. If you have got them involved, did they approve repairs, give you the option or say that the trailer is a total loss??? If a total loss, you may be able to buy back the trailer and then repair as a "rebuild titled vehicle"... That opens another possible "can of worms" but we're not there yet....