How long will you be camping? It might be easier to just convert the propane system to be able to connect auxiliary tanks to supplement your propane. How many 20 pound bbq propane tanks would you need to have to make this trip work? The bbq tanks can be exchanged at almost any gas station or store in FL, or they can be refilled, and are easy to carry.
I figure if you take out two generators and their gas cans that you could fit 3 bbq tanks in their place.
The soft start things work. They are meant to lessen the power surge needed for starting only, nothing will reduce how much power the AC needs to continue running, so the little one 2000 will not run a 13.5 btu AC even if you can get it started. Generally you want extra capacity on the generator so it is not running at near 100% just to power your AC. A 50% load is more ideal.
Do not take it to an RV mechanic necessarily, this is not an RV thing, it is HVAC or electrical, foreign to most RV mechanics.
Any common every-day electrician will be able to install this as it is simple simple for them.
Any HVAC guy can also install this. Call around and take RV to them, they might be willing to do this, but you picked a bad time of year as HVAC guys are in peak demand right now.
If your brother-in-law is handy then he should be able to do the install. It is not rocket science.