I had a slow leak on a 1979, which turned out to be at the stem on the water valve on the toilet, not the connection. Since you can't see the back of your toilet, your leak may be in the same location.
For such a problem, many people replace the whole toilet. I bought a replacement valve, expensive at $50, and just replaced that.
I've attached photos of the worn out valve which fell apart in my hand, and the finished job, looking thru and access panel from the bedroom to the back of my toilet. If you don't have such a panel, I suggest you make one.
For me, where the water line connected to the toilet, it was impossible to get apart. I cut the line, and after the repair I installed a new fitting at the valve, a 90 degree angle, and a short piece of pex tubing to complete things. All Flair-It fittings which are easy and almost foolproof to use if you buy the special wrench.
A few more tips since you are new to RV plumbing: You will need to replace the foam rubber seal at the toilet flange. Cheap and easy. Also, I could not get the fitting to stop leaking where it threaded into the new valve. Tried teflon tape, pipe dope, everything. The final solution, JB Weld used as pipe dope. Put it on the threads only, and let it set up before turning on the water. You have one chance to get it right. Should the toilet need to be removed in the future, that new piece of pex I spliced in will be come apart easily enough.