I dunno if they have it up there, but it's called flexwatt heat tape and it comes in 3", 4", 11", 17", 21" widths and up to 100 feet long. You hook it up to an electrical chord and add a dimmer. BAM! You have adjustable heat for whatever you need.
I just use a sunbeam brand therapeutic heating pad from the drugstore for $15 and it keeps the temps perfect in my roachbin. Just make sure you get one without auto shutoff.
I have my Dubia's in a plastic tote. Can I use a Exo Terra Heat Wave Desert Vivarium mat Heater 120V? I thought I could stick it to one side of the tote. But Im not sure if it will make enough heat or to much heat for the plastic tote.
Roaches will drown in a water dish. alot of people use water crystals but I personallly just throw in oranges and other juicy fruit and it seems to be fine mind you that my colony is not massive yet.
I would follow an already verified to be good gutload instead of making what you think the roaches will like -- I am not so sure about the pears or banana.. oatmeal is iffy if it has sugar, and it depends on the lettuce.