There's a bag specially for the PF500 and PF800 http://www.ampeg.com/products/accessories/
aaand, HOTTER THAN HOT, THERE'S A PF410HLF COVER IN THE MAKE: http://www.thomann.de/nl/ampeg_cover_pf410hlf.htm
THIS IS NOT OFFICIAL, I HAVE NO CONNECTIONS TO NOBODY, BUT...CHECK IT OUT!
Furthermore, some extra pics of de PF800 bag: http://www.thomann.de/nl/ampeg_pf_500_800_bag.htm
(This website is by the way also in english.)
I'm sure other (web)shops have these items to sell.
Take your pick!
If covers and bags wont do the trick for you, then you'll have to go flightcase.
And all of this IMHO, IME and check it out yourself...