I've been working on my 251 models for a while now — I do a little at a sitting as I get time.  The three on the left are a 251d modification I made of a print and build kit from papertigerarmaments.com.

The one on the upper right is the 251c kit straight from the print file with my own modification of open rear doors.  I find my paper AFVs fight just as hard as the plastic and resin ones do.  They have the added advantages of being cheaper yet more durable.