Road grime in wood bed

[ThreeQuarter]

I’ve driven the ‘68 in the rain once now and through some puddles on a different day. Both times I noticed I’m getting road grime/muddy water sneaking into my fleet side wood bed in front of the wheel wells. It’s clear to see why this is happening—because the bed wood and the metal strips catch the water as it’s running down the inside of the wheel tubs. Also explains why this pickup’s original bed was rotted in the pattern it was.

So, does everybody with wood beds experience this? My first thought is to use strip caulk to seal the gap, but before I try to fix it, I’d like to hear from anyone who may have already been down this road. What’s the best way to deal with this to keep your bed clean and preserve you bed wood?