That's happened to me many times. The camera is rotating on the plate when you have it in the portrait orientation. Don't tighten the screw too much. There's someone in my camera club who had the same problem and almost completely stripped out the threads in the mounting hole on the bottom of the camera. An L-bracket would be a solution. There are different companies that make them such as Really Right Stuff. Benro and Sirui make them for the D800/D810.

Benro
https://www.samys.com/p/Tripod-Accessories/LPND800/LPND800-Quick-Release-L-Plate-for-Nikon-D800-and-D810/173787.html

Sirui
https://www.bhphotovideo.com/c/product/1024714-REG/sirui_bsrtyd800l_l_bracket_for.html

Just got back from 8 days in Big Bend. Did a lot of hiking. An awful lot of it is desert but the cacti were in bloom. The trails that stand out were The Santa Elena Canyon (not the overlook), The Lost Mine Trail, The Window Trail, Burro Mesa Pouroff. We hiked others but these are the ones I liked most. The Old Maverick Road is pretty rough. If you're driving a regular car don't even think about that road. Chisos Basin is the best place IMHO to be based out of. Higher elevation makes it noticeably cooler. There's a Really nice restaurant, running water, flush toilets, camp store, rooms to rent BUT campground and rooms filled up every night we were there. Many of the above amenities are NOT available in the other campsites. If you are traveling in an RV, Chisos is only open for 20ft. max. You can't make the curves with anything longer. I did pretty well with a 24-120 f4 on a crop sensor. I'm sure some will say you need wider but I found it was pretty easy to get far enough away. A couple of sunsets were really good but the evening light on the mountains at Chisos is not to be ignored. We are both 70 and pretty active but declined the Emory Peak Trail because of the 8,ooo+ feet altitude. Chisos is also good for the night sky because it's well away from any city lights and they ask that people refrain from use of artificial lights after 10pm. We sat at our picnic table for a while each night just to see the incredible star show.

The translum is a great material, I also have several types of flexible sheeting material in translucent, semi-opaque, white, etc. from Tap Plastics here in San Jose. i.e.

https://tapplastics.com/product/plastics/plastic_sheets_rolls/polypropylene_sheet/559

These are great for sweeps or diffusers, etc. easy to cut to needed sizes and cheap enough to cut to needed sizes.

I also purchase acrylic boards in black (other colors available) for product photography. With care, they stand up to continued usage and if scratched can be used for other purposes. Initial costs are very reasonable, and they come opaque and translucent as well. Custom orders are always welcome, so if you can dream up a use, they can cut the pieces to make it work.