At camp the first thing to come out of the truck is the yeti cooler and my dog uses that to jump up to the tailgate. Ive got 4 frontrunner boxes stacked and ratcheted in the back of the bed and she will usually hop up a duffel or whatever is lying there and then those to the top. It took her some getting used to, but we live in the truck so she figured it out fast. She’d rather be in the camper than in the cold and knows very well its her home. Been doing it for months now in and out without me, I just remember to pull the panels for her and if I forget she’ll remind me. The height of 3 or 4 boxes stacked really helps a lot to get all the way up to the tent, plus shes a smaller/medium sized dog. I also use the cooler for myself to step up to the tailgate and on whatever is in the bed to get up into the tent. I carry a ladder for the tent, but prefer going in from the bed, especially in cold or bad weather. I only really use the ladder if the bed is jam packed with gear.
As for your dogs, I would try to get them to go up things you already have in there if possible but realize all dogs are different. For my last dog I had a plywood ramp that slid-out to get him up into the bed (pre-GFC). He was 100lbs and getting old, though he refused to use it or anything else I tried and after he couldn’t jump I carried him up it till the day he left us. Im very glad this one has it figured out, especially when space is precious in a short bed, I dont need extra stuff taking up more space so everything must have multiple purposes. I also use the cooler or frontrunner boxes as seats around camp as well.