Ridge beam sizing for an 8'6" x 20' tiny house
Massive overkill.

If you are content to give up the vertical height this monster takes, simply extend the line of its bottom out to 1/2" from the top face of the rafter and cut a lot of (looks like 24) 1/2" plywood triangles. 



Glue and screw to the face of the rafters (which you'll cut to meet in the middle.) You can cut a scrap of 2X to fill the bottom void, but it will make little difference for this scale.

You don't need a ridge beam at all. You just need to keep the ends of your rafters from spreading, and the gusset will do that nicely for a house this tiny. If you want to cut the points off and use a 1x4 ridge board on top, sure, fine, structurally irrelevant.

This is particularly important since you are putting it on a trailer, so excess, wasteful weight is a detriment.

Which might be a good reason to talk to a licensed engineer (I'm merely a vernacular builder, but I have sheds bigger than that with less roof structure that have taken snow loads for 20+ years) about how to minimize the structural overkill to suit the scale of the house. You've already given building codes for houses the brush-off by putting it on a trailer - perhaps you should learn more about how trailers are efficiently built before you give up a lot of interior volume and add a lot of weight for structure you don't actually need.

If time is not too much of the essence, you could potentially get some engineering class interested in taking it on as a class project.

If you are open to a change in roof style, the traditional mobile tiny house (the Gypsy caravan) features a stylish arched roof structure (you might need to consider altering the traditional exterior detailing in light of what speeds you'll tow at.)