Here is what I do with just about ANY cut of beef but London Broil on sale for $1.50 or $2.00 a lb is better than rump roast.

Crockpot it with the Montreal steak seasoning (I get the large container at Costco for cheap) and a few cups of water and let it cook for at least 8 hours. It comes out tasting like the BEST roast beef you have ever had without all the marbling. I then later use the soup base for roast beef soup - with green onions and peppers and green beans - very very tastey!