All the fireplaces I've seen use either "candelabra base" incandescent bulbs or "T-6/T-10 base" halogen bulbs. Usually removing the trim around the fireplace will expose screws that hold it in position. Removing those screws will allow you to pull the fireplace.
There are several manufacturers of RV fireplaces, actually there are several distributors of RV fireplaces around the Elkhart, IN area. Most (if not all) of the products are actually made in China and replacement parts are very difficult to obtain. Trekwood doesn't sell "parts for fireplaces" that old, but they do have replacement "fireplaces for sale"... The cost for the 2007 Laredo fireplace is listed at $907. I wouldn't consider that a bargain
You may be able to remove the bottom grate/vent from the fireplace with it installed without having to remove the entire fireplace. Somewhere on the fireplace, either on the back, a side or possibly under that lower vent, there's an identification sticker with model/part number.
Do you have an owner's manual for the fireplace? If not, have you searched for "RV fireplace" on Google? If you don't have a manual, you may find an image on Google that would lead you to websites that have fireplaces that look like yours, leading you to a manual that would give you the information you need on how to replace bulbs....
Good Luck