There is nothing wrong with covering the head with something that does not touch or stay above it such as an umbrella, tent, car roof etc. while in the state of Ihram.

If the pilgrim does any of the restrictions of Ihram deliberately with no excuse, he has sinned and the violation is of three types: 1. That for which there is no Fidyah, which is entering into a marriage contract. 2. That for which the Fidyah is to sacrifice a camel, which is having intercourse before the first stage of exiting Ihram. 3. That for which the Fidyah is to fast for three days, which may be done consecutively or separately, as he chooses; or to sacrifice a sheep of a type that is acceptable for the `Eid sacrifice, or one-seventh of a camel or of a cow instead, and to distribute its meat among the poor and not eat any of it himself; or to feed six poor persons, giving each one half a Sa` of staple food. He is given the choice between these three options if he removes any hair or nails, puts on perfume, touches a woman with desire (but without having intercourse), if a woman puts on gloves or a face-veil, or if a male puts on form-fitting clothes or covers his head.

There is nothing wrong with wearing a belt over the izar (waist wrapper) of the ihram. What the scholars mean by wearing things that are stitched is that which is made to fit the limbs and is worn in the manner in which such garments are usually worn.