I didn't want to put a hole in the side of the van either so I used one of these:

https://www.amazon.com/gp/product/B073622GFZ/ref=ppx_yo_dt_b_asin_title_o04_s00

Then I took the white back off (one of the pictures shows with this removed) and bolted it one of these:

https://www.lowes.com/pd/TayMac-2-Gang-Gray-PVC-Weatherproof-New-Work-Old-Work-Standard-Switch-Outlet-Wall-Electrical-Box/4005491

with this on the face:

https://www.lowes.com/pd/Hubbell-TayMac-2-Gang-Rectangle-Plastic-Weatherproof-Electrical-Box-Cover/3773447

And bolted that to the frame under the van. I mounted one of these cable glands on the back of the electrical box and another in the floor of the van:

https://www.amazon.com/gp/product/B08MYPBJ93/ref=ppx_yo_dt_b_asin_title_o07_s00

Then I used 10-3 gauge SOOJ cable from the box to the gland and into the vehicle. Totally water tight, hidden and even air tight when done.

Inside the van, I ran the cable into another gland, mounted on this:

https://www.amazon.com/gp/product/B07GST347D/ref=ppx_yo_dt_b_asin_title_o04_s00

Then I used a pair of DIN rail mounted dual-pole breakers - one for my solar panels and one for this shore power. Grounds are all tied together on a Victron Lynx which is then also tied to a ground on the vehicle frame.

Whew, lots of stuff, but it seems to work great and is very sturdy. I used the glands and pex for my hose to water line connection into the van as well and it worked great too.