I don't think that a 5w tender will replenish what your camper's parasitic loads will consume. Not to mention that it will only be charging if you have bright Sun.
If you have a battery disconnect switch, then you should be ok to maintain a charged battery.
You'll need a lot more than 5w to charge a battery. I can't tell you how much wattage you need as I'd need lots more info.
2000 Cherokee 29BH with 6V batteries, LED lights & 400 watts of solar power, flipped axles and raised. 2007 Tundra 5.7L DC-LB with lots of mods. C-co, 8/158th AVN Maint.