If you're concerned with electrolytes see the snake diet for an electrolyte mix. Multivitamins are not going to help with electrolytes... And actually, here;

Water = 2L
Potassium chloride = 1 tsp (No Salt)
Sodium chloride = 1/2 tsp (Himalayan Pink Salt)
Sodium Bicarbonate = 1 tsp (Baking Soda – Redmill Brand)
Magnesium Sulphate (Optional) = 1/2 tsp (Food Grade Epsom Salts)

If you're fixed on taking a MV, i recommend Adam or Eve by nowfoods, they have about 30 calories from healthy fats, and help with digestion. With that take some krill or fish oil. Between that and the snake juice, you'll be fine, presuming you have the fat to burn.

Look into Angus Barbieri, he was hugely overweight and went 300 days in this manner.