Personally,
I would not use aspen for any snake from a tropical environment.
Apen is a very drying substrate.
Cypress would be a better choice, and it's very cheap.
Just get the cypress mulch sold at any garden center...I don't know where you are, but in the spring here (ohio) it's sold for dirt cheap at all the gas stations.
In my experience as a former zoo keeper, the general rule was snakes from dry climates were kept on aspen, and snakes from humid climates were kept on cypress.
You should not have a need for damp moss if the snake is on cypress and you have a nice large water tub.