On any camper if the eyebolt and the anchor point are too far away from one another there is too much lateral strain being put on the eyebolt. I see you have a flat washer and nut beneath the camper and you stated you had a plate of some dimension mounted inside the camper where I assume you have another washer and hex nut.
As noted, if the wood is soft from water intrusion then that is probably going to call for some repairs and/or a relocation of the eyebolt holes on both sides.
However, if that is not the case then I would ask how large the plate inside the camper is and....I would suggest you add another plate between the external surface and the flat washer as seen in your pic. It should spread the sideways torque better....and as I mentioned above, there is a "sweet spot" for mounting things when tying down the camper; too far apart and any axial movement will want to pull the eyebolt sideways. If the mounting point on the truck is straight down, that isn't the most ideal mounting situation either.
If you use aluminum plates above and below the floor (inside/outside) be sure to use Pro-Flex or something on the external plate-to-camper. You might have to add an additional bolt/nut/flatwasher/lockwasher to the two plates to help prevent any lateral movement.
Just a quick question; are you using FOUR eyebolts and are you using standard turnbuckles or do you have the Happijac system? Can you post a pic of the four eyebolts & turnbuckles from a short distance to see the ANGLE the turnbuckles are on and show us where they are secured to the truck.