We stayed at the Belum Eco-Resort for 3 days/2 nights. Note - you have to book a package to stay, at least food but you're really going in order to take a tour; so I made the reservation initially through a website but finalized over email/paypal.
The drive to Royal Belum was very pleasant, a nice road and the jetty where you meet the boat is modern and has lots of information on the Royal Belum park. Driving in Malaysia was easy, I imagine we could have taken a bus but having our own car was much easier. We left the car at the jetty, 5 MYR ($1 USD) per day. The boat showed up on time and one other family joined us on our trip back to the island.
The boat trip is very nice, a leisurely tour on a houseboat, and is a nice perk to staying at this resort. I also looked at the other Belum Resort, but I'm glad we chose this one. The Belum Rainforest Resort is right along the main road, and while I imagine it's more luxurious you wouldn't feel like you're in the jungle looking at and hearing the road all day...
The resort has a beautiful main lodge with a big veranda overlooking the lake. The chalets are simple affairs, but we liked their rustic nature. There is a short walk between the chalets and main lodge with a few stairs, be aware if anyone has a disability.
Meals were done family style, and we thought the food was very good, traditional type cuisine for dinner, fresh caught fish, curries, etc.. A mix of western (e.g. french toast) and malay (noodles) for breakfast. Bring your own alcohol as they don't have any; but they do offer water, tea, coffee (instant) as much as you like.
They took us out on the lake the night we arrived for a little bird watching/sight seeing, and we did the full Royal Belum tour the next day. We were very fortunate to have a family who spoke english and malay along for the tour, as our guide spoke some english but they were able to ask questions and translate more directly. The lake is beautiful, we saw rafflesia, waterfalls, and some hornbills. Sadly, no elephants, but they're wild animals... Visiting the Orang Asli village was interesting.
The resort's owner Steve is clearly very passionate about the rainforest and environment. I liked the documentaries they had for us to watch; and Steve was able to share a lot of history about the region. Sadly, logging and lack of care for the environment has been drastically impacting the park and rainforest. I highly recommend this place and visiting the rainforest.