Guild Wars 2

Checked the wiki and couldn’t find the answer.
http://wiki.guildwars2.com/wiki/Siege_weapon

There is a despawn timer on them?
How long is the timer?
Siege weapons that are a part of a tower upgrade are exempt? (Canon, Mortar)
There a siege weapon cap? Per map?

30min timer before siege despawns, you just need people to hop in them for a second to reset it and you can keep them forever.

Not sure about siege cap but there is one AFAIK.

As this thread is still fresch, I would like to ad a few questions I found no answer for:
Has anyone a statistic at hand what attack on which siege weapon does how much dmg on average? Maybe also some info on the “hp” of the weapons and how regular to upgraded weapons compare?
I think this is vital info and it would be much appreciated.

All I found this far is a post with in detail description of the weapon skills and their cds.
http://www.ign.com/wikis/guild-wars-2/Siege_Weapons