It is practically a given that I put onions in with the chuck. I like standard yellow (they have less water in them than Vidalias; all that water is what makes Vidalias sweet so I like those raw but if you have a bunch use them).
A favorite treatment is to use a rub called quatre-épices. There are a few variations on the ingredients depending on what part of France (or Quebec) you're in but if you'd like to try it it is very simple and works well with chuck and onion. I add a little fresh garlic as well and a wine reduction--both are worth doing, imo.
Quatre-épices: Combine 1 T freshly ground white pepper with 2 t ground clove, 1 1/2 t ground nutmeg, and 1 1/2 t ground ginger. White pepper is preferable--use black if need be but white really adds to this.
Salt the beef all over. Allow to sit and get moist while you mix the spices. Apply the rub. Cook as you're planning.
Meanwhile, mix in a small pot on the stove 1 cup cheap white wine (I use supermarket 'chablis' like Inglenook or Taylor, 1/4 c cheap dry sherry (like Taylor--NOT cooking sherry, however), and 3 T balsamic vinegar. Bring to a boil then lower the heat to medium. Reduce the mix till it is about 1/4 cup; reserve.
Most of the onion family will sour if you prep them too early so slice the onions within 15-20 min of use. I use 3 lbs onions for a 4 lb hunk of chuck (most often chuck eye). Add 4-6 cloves minced garlic to the onions.
When ready to foil lay half the onions and garlic on a large piece of HD foil (be generous with the foil); drizzle with half the wine reduction. Lay the chuck on the onions. Drizzle with the rest of the wine reduction and top with the rest of the onions and garlic. Bring the sides up of the foil and lay a foil piece on top. Crimp the foil together--leaving headspace and space around the meat--so that the meat is sitting in sort of a bowl. It and the onions will exude plenty of moisture which you don't want to lose--much of which will absorb back into the meat. Alternatively use a small disposable aluminum pan and cover tightly with foil.
Just a thought.