Congrats on the new burm. Your cage size sounds fine for him and should last for at least a couple of years since males don't get much over 12 ft anyhow. Youmay want to upsize in a couple of years, but you are fine for now. If your burm is underfed you should get him on a good feeding schedule. No need to over do it since that would tax his system since he is not in top top shape. A good feed every 10 to 14 days should be fine and he will come back up in weight before you know it. A good rule is "poop out rats in". At 8 ft. he is actually ready for 3-5lb rabbits so the collasal rats will be your best bet for now, but I would order rabbits when they run out.
Your temps sound fine, and seeing as it is 3ft. tall you should invest (about5 dollars) in an 18 gallon sterilite tub (model 1815). It will help with the humidity greatly and also give yuor new snake a place to go and soak. No need to fill it up completly either. I fill mine half way and then he can't overflow it. As for substrate, I would switch to cypress mulch, or aspen shavings. Both have good but different qualities. The cypress will keep the humidity higher but is not too absorbent. The aspen will need to be misted heavily when you first put it in since it comes fairly dry, but has excelent absorbency which you will learn to appreciate when the pee comes. If you have nto had a burm before you will not understand till you see the "load" after a 5lb. rabbit. And I know from experience that cage carpet may seem easier but it is really not too good in the long run.
Here is a link to a gallery that shows my burm setup. You can see the strilite container is put to good use here by my 12+ft. male.
http://www.thealbinoboa.com/gallerie...%20around.html
Have a good one.
David
