Re: transport jetski with cabin cruiser
Different states have different laws on this subject. However you could get a CDL with a doubles endorsement, and get your rig classified as commercial. You'll be paying a ton to do that and a ton more in insurance, but it would work.
to pull doubles yes get the doubles endorsement not sure if its cdl a b or c, might even be chueffers. it wont have to be classified as commercial because then you need paint your DOT numbers on the doors. also wont be cost effective if your needing to get a cdl.
i see 3 options at this point
1. a gooseneck would be the way to go if you dont mind hacking away at your trailer, then tow the jetski behind.
2. you could just modify the trailer, pull the toung off weld in some cross members to put the jet ski on ahead of the boat and adjust axles accordingly.
3. take 2 vehicals, after reading that your 100 miles from nearest lake, with a second vehical getting 20 mpg thats about $40-50 round trip, not cost effective again.
i would probably find away to do number 2 since dockwrecker has explained 2 trailers and 1 truck at a launch is not fun.