jacket for dog with a weird build

pretty much what caption says. my dog is a super mutt (according to dna test when we rescued him), and his body proportions reflect that lol. most jackets that fit his body are too tight around the neck, and if they fit around his collar/neck area they are way too loose or long on the body, and he’ll end up pissing all over it. he’s at ideal weight according to the vet so i don’t think it’s an issue of him being overweight. any recommendations? we live in a cold climate (forecasted single digit temps (F°) next week) and he spends two days a week outside all day at a camp, as well as walks in the woods multiple times a day, so it needs to be fairly warm and waterproof as he’s a short hair dog.