The SB is about a nut being able to back off and come loose, thereby leaking fuel. I'm not a builder, so I have no idea how it's put together. Wouldn't it be prudent to at least remove it if need be and look? Obviously do the fix while it's open. I know it's a lot of work, but the A&P that did the pre-buy for me seemed to think it was extremely important. He's done pre-buys on dozens of RV's.
I just want to be safe.
I am certainly not trying to talk you out of it. You should understand what the issues is/was however.
The nut did not back off. What happened was the builder didn't know what they where doing and when they tightened the main fuel line, they did not have a wrench on the bulkhead fitting to hold it. The bulkhead fitting rotated and the pick up tube rotated along with it, upwards, lifting it off of the bottom of the tank. This led to a fuel starvation accident.
This can only happen on the left tank. On the right tank, the fuel pick up would rotate down, not up, if you tried to tighten it without holding the bulkhead fitting.
Anyway, some believe every SB should be adhered to, regardless of why it was issued. If you're an A&P with your butt on the line, your going to recommend it be done.
If it where my airplane, I would do a useable fuel test. Check the pickups for proper orientation, and then mark the bulkhead fitting with a sharpie line to the rib so at each inspection interval, when I check that fitting and hose for security, I can see if the bulkhead fitting has moved. I would not remove the tank just for reasons of the SB.
All that said, you need to do what you feel most comfortable with. It is your butt....