HM hydration --WWBTD?

Okay, I know you're supposed to figure this out a long time before the race, and do nothing new on race day, but.....I'm running a HM Sunday in Cambodia. Expect hot, humid conditions, although the race starts at 6:30ish, so it could be worse, and it's what I train in. Just found out that only water will be offered on the course.....again. This happpened last year but thought it was a fluke. Last year I cramped quite badly in the last 2-3 miles and had cramps all over my body a few hours AFTER the race--suspect my electrolytes were messed up. This year I brought two gels with electrolytes for the express purpose of this race and accidentally used one of them on a long training run (thought I had three and I didn't). I can't buy another electrolyte gel here. Assuming I can't find one at the pre-race expo (can't remember; last year got there late), should I.....

1. Just take the gel and hope it's enough with the water on the course.

2. Bring a bottle (600 ml) of my own electrolyte drink in a hydration belt. Plus is that it's the drink I use on all long training runs (nuun), and I could then alternate water and electrolyte the way I normally do. Minus is weight, balance (it holds two bottles and the only comfortable way to wear it is with the bottle to one side) and comfort (makes me hotter, tough to get race number on, etc.). I will probably take the gel anyway.  I've packed the tablets; might see if they have a one-bottle belt at pre-race expo, if not, WWBTD?

Normally on a long run of 90+ minutes, I alternate nuun and water at about 15-minute intervals, sometimes 10 toward the end if it's getting really hot or I'm running hard. The race will give out small bottles of water every 2.5 km; for me this is in the 10-12 minutes range; hoping to run about 1:30.