As a suggestion, making an alternate reservation would be a smart thing to do but don't give up on Fort Wilderness if that's where you really want to go. We tried to make reservations many months out as well and was booked up but kept trying on the phone and sure enough about (3) weeks away and just when we called, they had a cancellation so we managed to book it for a weeks stay with an excellent site as well.
Unless you're looking to shake down your ride and a few years off its' life, do yourself a HUGE favor and don't take either one.
I ALWAYS, ALWAYS take 126 west to Ventura, then the 101 North and when you get near the south bay area, you have several options to cut over. Advantages are scenery, cooler temps in the summer, smoother roads and pure enjoyment! Of course this comes with extra fuel costs and additional time to drive it but as the saying goes, it's not just the destination it should always include the journey!
You might want to try Temecula Valley RV located in Murrieta, Ca..
Talk to Eric, one of the owners.
Have not had remodeling work done there myself but have talked to another friend that did and was very pleased with the outcome.
Might want to try the following for your problems:
Redlands Truck & RV
They come highly recommended in the RV industry in SoCal and probably less than an hour from you now.
Mobile guy I've used in the past:
Unger's Mobile Fleet Service
Hope this helps
If nothing available in St. Pete area, you might try Holiday Cove RV Park in Cortez. We have stayed there several times and is a very clean and pleasant park in a nice area. Owner park that rents out spaces, a little pricey from November on but might be to your liking. Drive into St. Pete is about 30-40 minutes across the Sunshine Bridge.
Have a nice trip!