Slides on truck campers

I heard the recommendation for jacks down before slide operation applied to motorhomes, where body transfer twist between the axles.
I deployed slides on my campers hundreds of times with jacks up.
Both my campers had similar build with metal slide tracks pushed by gears.
The upper slide corners have about 1" clearance to the wall and that is what can close with uneven jacks extension.

^ Agreed and good word of caution. Just never occurred to me that they would be a limitation.

Grit dog wrote:

That seems strange. Means every time you stop for lunch or a quick sleep you have to run the legs down to the ground to run the slide out?

Well no, our camper is fully usable with the slide in, don't deploy for lunch/quick stops. Been a few overnighters where I only dropped jacks on slide side to run it out. Have never deployed slide with jacks up.
As jimh425 alluded to ours is also a 2001- slide mech not so much the issue, the large full wall square hole is. Structure isn't what might be found in newer units. Also easily racked.
I wouldn't hesitate to deploy our slide on flat slope but my point, as I gather OP new to T/Cs and possibly an older unit, was only a caution on using slide regardless of slope. If OP has manual and it states putting jacks down I would heed.

I think the intent is leveling the camper before running out the slides is the preferred approach to avoid possible drive issues.

Can you extend the slides without leveling, sure. Might it cause uneven wear or jamming, possibly. Can you drive with a slide out, apparently so :-)

On the other hand, slide technology has come along way since Fleetwood made TCs. I know Host has changed a few times since then. It's good that Fleetwood warned people.

AnEv942 wrote:
Some camper mfgs recommend extending the jacks before deploying the slide. Ours being one.
Not lifting off truck but down enough to support/stabilize the structure as slide goes out and its cantilevered weight.

That seems strange. Means every time you stop for lunch or a quick sleep you have to run the legs down to the ground to run the slide out?

Your question is totally open ended. But in my experience, I’ve had no trouble on slopes, either longitudinal or cross or both...on the truck. Not sure I’ve ever run the slide out when it was way out of level on its legs. But it shouldn’t matter as long as you haven’t racked the camper structure out of square. Dunno if that’s even possible, as mine lifts on 3 legs all the time. One of the back jacks always needs to catch up.
I’ll presume you’re leveling the camper halfway close after you unload it.

I have no problem opening my slide when camper is on truck, even if truck is not level. and I also live on a hill. I figure the bed is pretty rigid, as well as the camper body is rigid, but combine the two and its got to really take a lot of "out of level" to cause problems.

Some camper mfgs recommend extending the jacks before deploying the slide. Ours being one.
Not lifting off truck but down enough to support/stabilize the structure as slide goes out and its cantilevered weight.

Heck, I've DRIVEN an hour with the slide out deployed on twisty highway without any ill effects. I have a rear view camera and evidently I do not check the passenger rear view mirror often enough. Ha!

So I'd say a slope in a driveway just sitting there isn't gonna hurt anything.