FWIW I've never had an issue with my March pump marching around. I just set it down and plug it in. Maybe the wood decking doesn't let it move that much.
How about the 3 and 5 gallon leaktite screw top lids at Home Depot?Bucket Companion 5 gal. and 3 gal. Screw Top Bucket Lid in Black-LD5GRLBK006 - The Home Depot
only $7.35 plus bucket.