tailgate lock for a c10?

[erikgto]

I just bought a 1986 C10 ShortWide Silverado.
I has a flush fibreglass bed (Checkmate I think) cover so you can still open the tailgate with the lid on it.
To open the lid I need to drop the tailgate and release the lid clamps on both sides.
To avoid getting stuff stolen out of the bed I want to be able to lock my tailgate.
Obviously handle relocators don't work cause i need to open the tailgate to open the lid.
Has anyone fixed this issue?
I can't find Pop&Lock's for '73-8'7 trucks, just the newer ones
The power locks systems out there are also for '98 and newer trucks....

So what does work here?