We have had some success here on the wet side if you try some of the following:

Grow the plants inside a tire or two. The black of the tire holds and absorbs heat.

Grow them next to a fence, concrete foundation wall, etc. In both cases the reflected heat really helped.

Place aluminum foil sheet around the base. Not only does it keeps the weeds down but reflects heat.

We even got quite a few nice ripe ones last year, even though spring didn't come until July.

Lastly, we buy pretty good sized plants to set out. Takes way too long, for us, to start seeds even in the house and get good harvests.