You should not need a "heat lamp".. unless you live in a cold house most people are able to keep these frogs with little or no out side heating help at all..
Its only a Ten gallon tank a simple 15watt incandescent or 20-35watt Compact Fluorescent Lamp should emit enough heat all by its lonesome. They are Nocturnal so little to no UVB is required.
Just Monitor your Temps Closely. Im sure the temps are not that far out of your range..

As far as under-tank heating for arboreal frogs goes.. Despite its usual lack of effectiveness given the need for tall enclosures.. In my opinion it also messes with their natural behavior. Arboreal frogs use their vertical habitat to regulate their body temperature naturally moving "to ground" or under brush to cool down.. being a nocturnal creature that retreats from the light and having to now unnaturally thermo-regulate itself by moving away from ground often causes bizarre captive behaviors..