You also really should cover the back and sides with something opaque. Helps them feel secure.

And yes, if you can't keep the temperature in the room your snakes are in at 80 or above, you need a second UTH...even on a 10gal. In face, I've found you get a better gradient with two UTH on a 10gal than on a tub or 20long.

Of course, you'll need to get two thermostats to control them both. That's why your temps (seemingly) are WAY too high! Dimmers and rheostats work only if your room temps don't waver more than a degree or two. If you can't afford the good $80 and $110 stats now, pick up two ZooMed ReptiTemp 500R stats for only $25 each and save up for the better stats.
Trust me, you NEED thermostats to be able to keep snakes. They are the difference between health and illness, and even life and death in power outage/surge times.