I have a Cruiser 5th wheel so I am not sure your trailer and mine are built alike, but the Cruiser doesn't have any grease zerks. In fact, the instructions from Lippert (who builds the slides) says not to grease the slides as it attracts dirt and grit which will cause wear.
If the axles have zerks in the center you might give them just a couple of squirts each year, but be cautious as you can force grease past the rear seal into the brakes.
Check your manuals, or get on Lippert's web site. They have lots of information.