I noticed that no one has answered your question yet... First let me qualify my answer by saying: I have never even been to Colorado (but my best friend used to live there--I hear it's great!). But, I am a REALTOR, and many of the rural areas I service have many lovely manufactured homes. When considering the long term financial/investment aspects (and these aspects ONLY)of you question:
1. A "trailer" is of no value (no matter how nice)--you are purchasing the land. It is NOT classified as "real property".
2. A "manufactured home" (one attached to a permanent foundation) will depreciate in value, while the land appreciates. How rapidly the depreciation occurs will depend upon the exact property in question. It is usually classified as "real property". This can vary from town to town--it's very specific.
3. A "modular home" (it never had a trailer hitch) will appreciate in value, but not as much as a site-built structure; as well as the land (of course). It is classified as "real property".
4. A "site-built" home (even a simple two room cabin) will appreciate along with the land. And naturally, it is also classified as "real property".
The above #s 1-4 are GENERALALITIES. Each option has different pros and cons. You may wonder why I've made such a point to note as to how a property is classified: "real property"--or not--is important due to local regulations and zoning, tax and insurance implications, etc. This is just the starting point. You need to find a local REALTOR in the area where you'd like to purchase (Colorado is just too big) who understands these important issues (it's a pretty specialized field). Feel free to contact me, or simply re-post, if you need further general information or clarification.
Lastly, you may also consider purchasing vacant land to improve as you see fit, at your own pace. Best of luck and happy hunting!