There are some good ways discussed here to clean or keep clean our vacuum filters.
IMO the easiest way to keep them clean is by using a dust separator. I use one and it is very effective at catching the dust and debris before it ever hits the filter. I can fill a 5 gallon bucket with shop waste many, many times before I feel the need to clean the filter - and even then it is barely dirty. The suction stays strong throughout.
There are many models. I use the Oneida Dust Deputy which costs less than $50.

Did you build a rolling cart for the ShopVac and the DustDeputy or do you have a 'fixed installation' and piping in your shop?

For straight sanding dust (sanding epoxy/glass, gelcoat, primer-surfacer), the filter (on the motor) and filter dustbag (on the inlet of my vacuum) together work pretty well.