I keep a folding telescoping ladder in my truck 24/7 and don't often need something longer than 18':
The Little Giant® Revolution™ was designed with the pro in mind. The Quad-Lock™ hinge and metal Rock Locks™ allow for quick and easy height and position adjustment. The Tip & Glide™ wheels help you move the ladder easily from job to job. The Ratchet leg levelers give you more than eight inches...
www.littlegiantladders.com
Unfortunately the packed length is just under 6' so the Rivian bed wont work for this. If the bed comes in at 55" then I don't think you'll get any decent size telescoping ladder in there without the tailgate down.
For extension ladders I plan on using a load extender. My second vehicle is a 170 Sprinter and this setup still wont be as long as that:
The E-Z Load Extender allows you to transport lumber, drywall, ladders, kayaks and much more by quickly and easily extending your truck bed or roof rack. The versatile design can be used horizontally or vertically and features 5-adjustable heights and a 350 lbs. weight capacity. This item is...
www.homedepot.com
I'm willing to compromise in whatever way to use an EV as my daily driver. It certainly won't be ideal for a work truck but I think the benefits of the truck outweigh the negatives.