I too would assume that you have a standard 7 blade trailer light connection. So here is what I would do which can also be done with a flat four coming from the RV.
Remove all the convertors and add on stuff between the RV's stock harness and the socket. Now you're back to where you were when you bought your rig.
Buy and install two separate sockets for the turn signal cans and wire your flat four, right and left turn signal wires to those lights. You will also have to install two more diodes for those lights.
If you buy a new towed and it has combined parking/brake lights, your good to go, if it has the separate brake/parking lights you just buy two new sockets and install them in the brake light cans. Simple and only two very simple and "reliable" electronic devises to install, the two additional blocking diodes.
If you are like me and use another vehicle that I use to tow the Sidekick with flat four wiring, it's good to go.
You have just had an example of K.I.S.S method applied to your problem.
PS; Nice rig, a couple we met fell into a deal on a Beaver, owner died, wife sold it for the balance on the loan, $103,000. Nice.