Widen the front, narrow the rear, max caster, add toe out, positive camber, raise center of gravity.
Front bar either full stiff or out depending on your chassis. Some karts like to flex and some like the bar in to jack weight in the rain. Axle will be dependent on chassis too. Some karts like super soft, some like super stiff.
The main thing in the rain is driving. Can easily be worth seconds. Charge the corner, crank the wheel to force the kart to jack and help use the front tires to slow down, drive off the rubber/racing line, don’t spin out.
Most people drive way too conservatively in the rain. You need to attack corner entry and then finesse the kart off the exit, modulating throttle and steering to keep from spinning up the rear tires.
Bring spare socks and rubber gloves to wear under your racing gloves. And a spare pair of racing gloves if you have them. Sucks to drive with wet gloves in the event it dries out at some point in the day.