I would opt to just go with bait for flounder
I tried some Gulp stuff, even tipped with bait, and it's the only species I've seen it fail miserably with. Did hear the scent dispersion with Gulp is severely limited in cold water
Sandworms, bloodworms, clam strips, and mussels.
Sometimes adding a tiny twister tail in yellow, white, pink, or green can help, but it's mainly a chum and present bait type of game for the tasty winter flounder.
Light tackle, akin to trout fishing gear, is all that is needed. Generally you are catching fairly small fish that average less than 2lbs. They do put up a good account of themselves, but generally fishing in shallow waters so no need for heavy gear.
I use my lightest fluke setups that usually see 3/4oz to 3oz bucktails/lead&bait offerings during the Summer.
Flounder have a small mouth so patience is key and a rod that gives a bit is a good idea if using braid. I do use Fireline and graphite rods, so you can use just about anything to catch them
Rigs I generally just opt for a store-bought ones and add a tiny twister tail to them when the bite is slow. With flounder, constantly bouncing the rig is key and a much more reserved hook-set will help you out as well.
Main tip is to chum heavily, but not too much that they just eat the free floating food and not your baits
Lots of concoctions out there for chum, but personally I go with smashed mussels and clam shells that we shuck and use for bait.
