1-I would put something on top of the radiator or under the speaker to block the heat if you are that close. Veneer will delaminate over time.
2-Velcro is a great invention. It may discolor a patch either on the rear or underneath the speaker but should be sufficient in strenth to hold a small strap. You may even be able to put it where the speaker terminals are. However, you could even tie to the speaker terminals? They are usually quite well mounted and shouldn't have any problems as long as the speaker wire isn't interferred with.
2-Velcro is a great invention. It may discolor a patch either on the rear or underneath the speaker but should be sufficient in strenth to hold a small strap. You may even be able to put it where the speaker terminals are. However, you could even tie to the speaker terminals? They are usually quite well mounted and shouldn't have any problems as long as the speaker wire isn't interferred with.