HCA: Hermit Crab Association

My crabs are currently in a 10 gallon and I have no problem keeping the humidity at 80% but I can only get the temperature to 70 degrees and I'd rather it be more like 75. The crabs were a bit of an impulsive purchase, I saw them at the beach in one of those stupid metal cages being sold in plastic boxes and I knew that was definitely not how they were supposed to be kept, so I took it upon myself to buy 2. I didn't have a lot of time to research and obviously they are a very difficult pet to keep. I bought 2 of the heating pads marketed for hermit crabs not realizing they were meant for the pathetic plastic critter keepers some people keep as permanent homes. They pretty much cover the backside of the crabitat but I'm thinking it's time to throw them away and try something different because they seem very low quality even if they do cover a decent surface area. If I do another heating pad what size should I do, and I was also wondering about using heating bulbs but I know a 10 gallon is small for that method and I'd really prefer not to cook my crabs. I was also curious about opinions on using UVB.

You will want to get a UTH by dimensions, not by what it says it should heat as far as tank size. Get one that will cover as much of the back of the tank above the substrate as you can. Some UTH's can be insulated over top while others (the sticky ones) can only be insulated around.
What do you have as a lid on your tank?

For a standard sized basic 10 gallon tank an 11x17 UTH is about perfect. I prefer the Ultratherms heaters sold at Reptile Basics. You can insulate them and easily move them from tank to tank with no issues.
Adding a thermostat will keep the temperature From getting too warm. It won't do anything if you don't have enough heating power from the UTH.

As curly pointed out, having a tight fitting lid is key to controlling temperature and humidity inside the tank.