i dont use a pump but have done some mud runs and they are great fun! the first one i did while i was on holiday in south carolina by my moms house. she volunteered at a water station and had my meter and strips there so i tested mid run. it was only five km so it was fine. i didnt actually need any carbs and finished a bit on the high side, if i remember right, like 160 or something. i think the strenuous running up mud hills and adrenaline kept me that way. at the other one, i left it in the lockers provided. on both i carried gels with me just in case but didnt need them.
i have switched to running mountain races in the last year and test through them about every 5km, which is annoying but what are you gonna do. in those i had to carry my insulin, testing kit and sugar with me, but im not submerging myself in water so its less of a headache.
good luck with your run!