Got my Dubia Colony starters today need bigger UTH?

[nukeswife]

Today I got my Dubia Starter Colony in the mail. I have an 18g sterlite tote (looks like this http://www.walmart.com/ip/Sterilite-18-Gallon-72-Quart-Storage-Box-Set-of-8/10401037) and bought a 10-20 gallon UTH but the thermometer I'm using says it's only 78.6º on the bottom where the heater is. The vent I cut in the top is roughly 8.5" x 4". It never got warmer than 87º according to the thermometer. The bin is in my living room on a wire shelf.
This is the thermometer I have http://www.amazon.com/Zoo-Med-Digital-Terrarium-Thermometer/dp/B000MD3MFA/ref=sr_1_2?ie=UTF8&qid=1383963488&sr=8-2&keywords=zoomed+thermometer

Do I need to get a bigger UTH or do I just have a bad thermometer?

 

[Sauzo]

The only way I actually found to really heat the Sterilite totes is by putting it on top of my boa cage under her radiant heat panel but even that only heats it to around 88-90 degrees. The best ones I found to heat were the Rubbermaids. Seems they are thinner on the bottom so easier for heat to get through. I'm using the 45 gallon Rubbermaid Roughneck tote with a 30-40 gallon Zoo Med UTH on a lamp dimmer set to around 1/4 power and I hit around 100 degrees at the hottest spot on the bottom of the tote. Just be aware if you use that tote, you will need to run a strip of packing tape around the top about an inch or 2 from the top cause the little ones can climb the sides of that tote but it's really easy to heat and its big enough to house a huge colony. I got about 150 females in there with babies and nymphs of all sizes all over, plus way too many males but I can't bring myself to give them a burial at sea aka toilet and my beardie isn't big enough to eat adults yet. Thermometer should be fine. I use a temp gun since that's pretty much what I check all my reptiles with anyways.

 

[nukeswife]

Thank for your help. I bought a 14g rubbermaid tote (my colony is only 35 total right now) and the small UTH I had is getting the hottest spot on the bottom between 93 and 101