i have a 20 gallon tank and this is how i keep my temps up
i have a 20 gallon UTH not quite centered but put a little bit towards the left side and a lamp with a regular 100 watt light bulb pointed slightly towards the left and it seems to keep it perfect.
my room temps are 74 degrees pretty consistently
my hotspot - 90-94 cool side - 80-84 humidity - stays around 48-50 ambient humidity and i spray every once in a while under favored hide (i move her and the hide and moisten the substrate and re-even it and replace the hide.