mrbrute, yes a 20 gallon long would work but believe me when i say this it is just a downward spiral i say this because this is how i started and i just recently swiched to some animal plastics cages.

with the glass 20 lg i was barely able to keep the ambient temp above 78 hot spot 90 with my ac set at 76 and an undertank heater with no thermostat (i know) so i ran a light bulb to boost ambient temps well when you do that there goes the humidity so you have to make adjustments and work to keep it regulated.

now i have a animal plastics t3 with two hides and a water bowl some flexwatt and the florescent light and my temps are a cozy 82 ambient and 90
on the hotspot and my humidity is sitting pretty at 65 with just the waterbowl no other rigging or towles or humid hides necessary.

i spent about 150.00 bucks setting up a glass 20long to get it where i needed it to be and still had to do extra work every two days to make it work. i could have used that money and bought an animal plastics cage first for just a hair more and not had to deal with the aggrivation of temp and humidity regulation which in my book and im sure in the snakes book is well worth the money. so in short yes it will work but in the long run spend the money up front for a t3,t8 or even their 3 or 4 tub rack and you, your wallet , and your animals will be alot happier I know me and mine are .
which ever set up you choose good luck and if you have any questions feel free to ask. i will post some before and after setup pics in a second