I agree you really should get a thermostat, a good one will range between about $60.00-$120.00. My cheapest one is a Johnsons and I got that prewired for $80.00 on reptile basics, my most expensive one was a Spyder Robotics Herpstat for $118.00 grounded with free shipping.

As for the holes, I just did one row about 1 1/2 inches apart across the top of the sides. Mine are 34 qt tubs. I also used black spray paint to black out the sides, back, and lids of my tubs, but you have to let them air out for about 3 days to get rid of the fumes. You can always try Cont-Tact paper from Home Depot for like $6.00 a roll, might be a PITA to do on a tub though.

Good luck!