I would do this on a smaller scale as a letterbox garden feature
Australian railway sleeper projects
Drought Tolerant Modern Landscape Design Ideas. DIY hard scape for water-wise gardening, pool decking, patio bbq area, porch, luxury curb appeal, front yard & back yard.
Fabulous Front Entrances :: Letterboxes with Panache — Glamour Drops
Our featured sleeper fence with letterbox feature. ♥
Just wanted to share a pic of the letterbox I made, from this site. Absolutely in love with it. I also put a couple of coats of intergrain ultra deck
Letterbox .. awesome handiwork .
Hardwood timber sleeper letterbox