you asked : "Can the 450D stand up to the elements from an around the world travel?? "
the real question you meant to ask is can it stand up as well as other cameras or what are the tradeoffs
1) I would suggest for just travel something more like the sx40 HS (non-interchangeable lens superzoom) - for convenience and it hides well
2) The lenses are more critical for standing up to the elements; and the deal here is yours are not weathersealed so you need to take care of them - in a raint / muggy environment plastic bags sealed when not on the Camera, possibly plastic covers draped over them, etc when on the body
3) there ARE covers / protection you can buy for the body or body / camera combination
4) yes the 50D is a better built body, the 5D is somewhat weathersealed, the 1 Ds or 1d are even better sealed; none of which helps if you drop it in the water. Cameras do not swim
And there's your trade off (forget concerns of theft - thieves have no idea what camera you have and will steal anything) - price cs weatherproofing. In my local craigslist there is someone selling a used 50D for $600 and t that price I would think good investment for someone like you (note: this is a much heavier body, being metal, but much more durable) but there is no reason that, if you pack it well, don't drop it, take care of it; it should stand up to the elements
Seriously, no one here lives with you, knows how you treat your equipment so we can't really help more than general guidelines; it is up to you to take care of your equipment and all we can do is comment about build quality / durability vs. personal preference