Ultralights
Suggest you join Doug Reeves' Vansairforce site -
Van's Aircraft RV Builder Forums and News. ¯¯VAF¯¯ and use the search function for 'long range tanks' or 'extended fuel tanks' or similar. Hundreds of threads - some with good links to commercial builders - others to sole private builders who have included extra tanks during build. Most give at least another 150-180 mins flying time.
happy days,