Transporting rocks with a trailer - easy? Dangerous?

Thinking of renting a low trailer to transport some large rocks (~50-100 each; not sure how much we can fit) but I’ve never driven w a trailer at all — let alone one w heavy, odd-shaped cargo. So I’m nervous about keeping up a reasonable speed (to not hold up traffic) while maintaining proper control of the vehicle and the load. How easy vs hard is this? And what do I need to prevent rocks from flying off? Should I stick w the truck bed if I can? Trip each way is ~35 min at normal speeds.