Both the rail/channel on the MH itself and the roller on the slideout have set screws holding them in place both fore and aft. They can be adjusted. If you undo the set screws on the rail/channel on both sides that keep the material from moving in the channel and do the same on the bars you see below the slide topper roller on the slideout, you can tap it in either direction.
You do have to be careful to not get them out of alignment and have the material roll up crooked.
2005 Safari Cheetah 38PDQ - 2009 Ford Flex
Me (Gatogonow), The Boss (DW), Honey Bunny, Maggie May and Mollie Kay (The Gatos)!