I use the Smith Little Torch for heating the cups for floating and fine positioning for the pad to the tone hole surface. It is available from J. L. Smith or jeweler's supply houses like Rio Grande. It is light and can produce a tiny flame that, with practice, you can work around pearls, felts, and corks without burning. It can also perform any soldering task you will encounter with a sax.
I don't know what you mean by sealing the pads. You mention a heat gun and clamps. Some folks, and factories, dream that clamping (or wedging) the keys closed and heating until the glue (or shellac) melts and letting it cool down will put a "seat" in the pad, float it into position, set the felt, and make the pads seal. If only this worked. This is fantasy student "Elkhart" style padding technique, like using a pad oven and clamps on flutes. If a playable result is obtained this way, it is very short lived.
You mention mounting the pads. I mount pads one at a time with the keys on the horn after dry fitting to be sure that mechanical conditions and pad thicknesses are optimized. I use a glue gun or shellac gun (thanks Curt), depending on if the player anticipates using the instrument where winter exists, and apply the adhesive to the back of the pad. Shellac is very poor at holding pads in freezing temperatures, but so are many hot melt glues. The ones I use I test under freezing conditions. I hold the horn in a fixture so that the tone hole surface is level with gravity and lets my glue backed pad sit flat on the tone hole while allowing the key cup to close and fit over the pad. I then heat the pad cup while closing the key from its operating point (pearl, arm, touch piece) until the glue melts and the pad is in the cup, and wait for it to cool down. I then inspect with a light and dental mirror to see if the pad is touching all the away around the tone hole at the same time. If it is touching all around it is sealing. If in doubt about the seal, I'll check with a magnehelic leak meter. If it is not touching I make creative use of heat and popsicle sticks, wooden ice cream spoons, triangles of felt or plastic (never metal), and a dental pick to manipulate the adhesive bed to allow the pad to cover all around. Always check by closing the key from its operating point. When I am satisfied with the installation, I move on to the next pad. I set linkages at this time, and always have the springs engaged, because the torsions involved effect the way the pad contacts the tone hole. When the last pad is installed, the padding is finished. I pay no attention whatsoever to the pad "seat" impression in the pad. I don't use cheap pads.
In the Coats article from the link above, mention is made of "doping" the pad surfaces. Almost all of the pads available for the past 20 years, except the untreated ones that carry claims of not sticking, have been treated to make them waterproof. This makes the leather treatments mentioned, which were developed when pad skin was not treated, obsolete. In fact many will cause these newer sticky pads to become even stickier.