Cleaning! Comfort cushion covers and pop top canvas

[Michael Minta]

Hi all. We took the van away on our second weekend and noticed, likely due to heat, that a previous owner must have smoked inside the van. So two questions if I may please:

Any thoughts on the best solution to cleaning/desmelling the pop top canvas?
and
Do the covers come off the comfort cushions...it’s clearly zipped on but no clasp to get hold off and I don’t want to false it open to never be the same again?

Thanks in anticipation.