Does it light
when you are on shore power. Make sure your battery
is charged. It takes quite a bit of power to have fan, igniter and get the gas valve to turn on. After your know battery
is good and gas is on, Check other appliances to make sure you have gas, Turn the thermostat on.
Listen close, 1) the fan will turn on 2) gas valve will turn on (no sound) 3)the igniter will work. Do you hear the igniter clicking? If not you need to purchase and replace it.
If yes, and it doesn't ignite, the igniter may not be positioned right or the gas valve is junk or for one reason or another not getting gas.
If you have a sight glass look to see if igniter is close to burner and if not get in there and ever so gently get it closer.