From the picture, they look like "Shark-bite" fittings, (which I've personally never cared for,) but a lot of people use them. I prefer PEX crimped fittings.
A bypass, (aka winterization,) valve is not a standard ON/OFF water valve. If you have a single bypass valve, chances are pretty good that it is a 3-Way ported directional flow valve which allows flow, or isolates flow, through the piping systems to allow water, (or anti-freeze,) to flow through the water lines but ideally not into the water heater reservoir. There are several different bypass valve set-ups used in RV's and trailers. You can have a one-valve, two-valve or even a three-valve winterization isolation valve setup. If it didn't have a means to isolate the water heater reservoir from the water lines, you'd need about 7 Gallons of AF instead of one. Flow is deliberately directional in a single vale setup, for the reasons listed above, so a standard water valve won't suffice in most cases. Also, NEVER attempt to turn the bypass valve while the water system is pressurized. It will destroy the valve seat, and usually only takes once. I would think that yours had been turned while pressurized at some time which is probably why it
leaks now. Your PEX tools will come in handy, but you will need a new bypass valve. Make sure you get a replacement that matches the one you have. There are several different designs out there with various end fittings. Be sure to source the correct one. They're only around $20 bucks or so.
Now, if it's just a bad Shark-bite fitting, that's easily repairable for little cost or effort.