More handbrake issues: 1995 Sierra

When the rear brakes get really wet from heavy rain or when launching my boat, the parking brake freezes when applied and won't let loose. I have to gun the engine and then it will let go with a loud crack. Only happens when
the brakes are wet and the truck sits for awhile. Any ideas for a fix (other than "don't use the parking brake when wet')? Suggestions? TIA. BTY; front disc and rear drum brakes.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.